DuPont and the U.S. Department of Agriculture are jointly developing a new test for lesser-known strains of E. coli bacteria that have become the source of increasing concern after recent outbreaks linked to contaminated fresh produce.

The new test will detect the so-called “Big 6” E. coli, which the Centers for Disease Control and Prevention says is responsible for about 36,000 illnesses a year in the U.S. Most U.S. food industry testing focuses on E. coli O157:H7, the cause of most reported outbreaks.

These harder to identify shiga toxin-producing E. coli, or STECs, “have been causing increased instances of food contamination and illness,” DuPont said in an Aug. 2 statement announcing the project.

“In recent years, other types of STEC have been identified as agents of food-borne illness, and these are a growing concern in the United States, Europe, Japan and food safety agencies worldwide,” DuPont said.

The new test will be based on ground beef but will also be applicable for fruits and vegetables, said Michelle Reardon, a spokeswoman for Wilmington, Del.-based DuPont.

E. coli can be found in the intestines of cattle, and sicknesses typically involved ground beef contaminated with O157. In recent years, the produce industry has come under heightened scrutiny after outbreaks stemming from tainted lettuce and spinach.

Earlier this year, shredded romaine lettuce contaminated with E. coli O145, one of the Big 6, sickened at least 26 people in five states.

It was the country’s first reported E. coli outbreak linked to O145, according to the Centers for Disease Control and Prevention, which described O145 as an “emerging bacterial pathogen” that can produce the same illnesses as O157.

The DuPont-USDA test will use DNA analysis to identify pathogens in food samples and is designed to be “rapid response,” Reardon said. The project is expected to take 12-18 months to complete and will be the first commercially available test for the Big 6 E. coli, she said.

DuPont already sells E. coli O157 testing systems to the USDA through the company’s BAX unit, which makes software and other technology used to monitor food pathogens.

Little E. coli testing beyond the O157 strain is done by the U.S. fresh produce industry. But tests conducted by Earthbound Farm, a San Juan Bautista, Cal.-based organic salad greens grower, suggest non-O157 strains are becoming more of a problem.

Among test samples this year, the “vast majority” were non-O157 E. coli strains, Earthbound Farm director of communications Samantha Cabaluna said in July.

The less common E. coli strains are “not a fully recognized issue in foodborne pathogens,” Cabaluna said.